1. Field of Invention
The present invention relates generally to the field of transmissive panels. More specifically, the present invention is related to the use of wire grid polarizers and wave retarders in transmissive panels.
2. Discussion of Prior Art
The U.S. Patent to Metwalli (U.S. Pat. No. 5,189,552) provides for an incidence angle light attenuator for light transmissive panels. Specifically, Metwalli teaches a method and apparatus for controlling light attenuation through a light transmissive panel that uses polarized film sheets positioned on opposite surfaces of the panel.
FIG. 1A illustrates Metwalli's light transmissive panel 10, such as a window or automobile windshield, wherein the transmissive panel 10 is covered by a film 12 on one surface and by a film 14 on an opposite surface. Each of the films 12 and 14 has a plurality of attenuating strips of different absorption axis of polarized films. Film 12 includes polarized strips 16 having an absorption axis aligned in a first predetermined direction. The strips 16 are arranged in generally horizontal, parallel rows spaced apart by sections of film strips 18 of absorption axis differently oriented from strips 16. Film 14 includes polarized strips 20 having an absorption axis aligned in the same predetermined direction as strips 16 and spaced apart by film strips 22 having an absorption axis oriented in the same direction as film strips 18. The strips 20 are aligned to overlay the film strips 16 while strips 22 overlay strips 18. The film sheets are oriented on the opposing surfaces of the panel such that light passing through within a preselected range of incidence angles passes through strips of common polarization. Light impinging on the panel at other incidence angles passes through strips of different polarization and is significantly polarized or may have varying polarization in order to provide attenuation within step changes.
FIG. 1B illustrates a traditional wire grid polarizers having a plurality of lines of conductive material running at nanoscales. For example, the spacing between the conductive wires is in the range of 150 nm. FIG. 1B illustrates a pattern formed by conductive wires 102 as applied to a nonbirefringant substrate 104. FIG. 1C illustrates a cross section of the wire grid polarizer shown in FIG. 1B.
One problem associated with the prior art, such as Metwalli, is that such setups, at a theoretical maximum, can only achieve 50% clarity at its clearest and 100% opacity at its darkest.
Another problem associated with the prior art, such as Metwalli, is that such traditional polarizers are made of organic compounds or iodine, which will degrade in exposure to direct sunlight over shorter time-spans (two years or less in their intended use in direct light).
Yet another problem associated with the prior art, such as Metwalli, is that they fail to achieve a mirror state at full opacity instead of a darkened state.
Further, the prior art, such as Metwalli, fail to provide a robust solution for selecting the level of light to transmit on a grayscale from near 0% to near 100%. In order to achieve a range of 50%-100% range with conventional polarizers, one must either manufacture one continuous polarizer with a plane of polarization in one direction then cut it into strips at differing angles and re-laminate them together in order, or one has to produce a continuous polarizer and stretch it (longitudinally in shear) until the plane of polarization approaches an s-curved shape. The former results in a large amount of waste material, takes a long time to achieve (and is difficult to automate) and results in visible “stripes” where the cuts were, even if done at perfect tolerance. The latter has proven difficult to achieve and must sacrifice some contrast ratio (ratio of clearest state to darkest state).
Whatever the precise merits, features, and advantages of the above cited references, none of them achieves or fulfills the purposes of the present invention.